1. Field of the Invention
The present invention relates to an image-pickup system including a lens apparatus with an aperture stop and an image-pickup apparatus that controls energization of an actuator for the aperture stop based on information received from the lens apparatus.
2. Description of the Related Art
A lens apparatus mounted to an image-pickup apparatus such as a digital still camera is equipped with an aperture stop (a light-amount-adjusting unit) driven by an actuator such as a stepping motor or a galvanometer. Such a lens apparatus controls the driving of the aperture stop in accordance with an energization instruction from the image-pickup apparatus. In this case, energization of the aperture stop is usually maintained in order to prevent the aperture diameter of the aperture stop from changing due to disturbances such as a shock given after the aperture stop has been driven to an instructed position (target aperture position).
When a long shutter time is set in the image-pickup apparatus, an energization-maintaining time of the aperture stop is increased, thus correspondingly increasing the power consumption. To cope with this, Japanese Patent Laid-Open No. 58(1983)-90626 discloses a technology of suppressing the power consumption by performing a so-called PWM control, i.e., intermittent energization of an aperture stop after the aperture stop has been driven to an instructed position.
The image-pickup system is usually provided with a function called small-aperture preview that enables the confirmation of depth of field in association with a set aperture value. When the small-aperture preview function is used, if electric power is always fed to the aperture stop for keeping a constant aperture diameter, the power consumption will be correspondingly increased. To cope with this, Japanese Patent Laid-Open No. 2002-156681 discloses a technology in which power supply is stopped to the aperture stop after the aperture stop has been driven to a set value by the small-aperture preview function.
However, there are various types of motors available as an actuator for the aperture stop, including one being good or poor in ability of holding its rotation position when energization is stopped, one packaged in a metal case and one packaged with a resin material, for example.
In this case, if the system is shifted uniformly to an intermittent energizing state or the energization of the aperture stop is uniformly stopped after the drive of the aperture stop to a set value as in the technology disclosed in Japanese Patent Laid-Open No. 58(1983)-90626 or Japanese Patent Laid-Open No. 2002-156681, the aperture diameter may not be kept constant or a sufficient effect for reducing the power consumption may not be obtained because of unnecessary intermittent energization. Further, since a motor packaged with a resin material has less heat-resistance, if such a motor is energized intermittently for a long time, heat generated from the motor may adversely affect the resin material.